Optically transparent adhesion layer to connect noble metals to oxides

ABSTRACT

A reflective layer for use in lighting devices and methods of forming the reflective layer are provided. The reflective layer may include a dielectric layer including one or more insulating materials. An intermediate layer may be formed on the dielectric layer. The intermediate layer may include one or more materials having a higher enthalpy of reaction than the one or more insulating materials. Because of the higher enthalpy of reaction, atoms of the one or more materials in the intermediate layer may form bonds with atoms of the one or more insulating materials. A metal layer may be formed on the intermediate layer to reflect light emitted from an active region of a light emitting diode (LED).

BACKGROUND

Semiconductor light-emitting devices including light emitting diodes(LEDs), resonant cavity light emitting diodes (RCLEDs), vertical cavitylaser diodes (VCSELs), and edge emitting lasers are among the mostefficient light sources currently available. Materials systems currentlyof interest in the manufacture of high-brightness light emitting devicescapable of operation across the visible spectrum include Group III-Vsemiconductors, particularly binary, ternary, and quaternary alloys ofgallium, aluminum, indium, and nitrogen, also referred to as III-nitridematerials.

Typically, III-nitride light emitting devices are fabricated byepitaxially growing a stack of semiconductor layers of differentcompositions and dopant concentrations on a sapphire, silicon carbide,III-nitride, or other suitable substrate by metal-organic chemical vapordeposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxialtechniques. The stack often includes one or more n-type layers dopedwith, for example, silicon, formed over the substrate, one or more lightemitting layers in an active region formed over the n-type layer orlayers, and one or more p-type layers doped with, for example,magnesium, formed over the active region. Electrical contacts are formedon the n- and p-type regions.

SUMMARY

A reflective layer for use in lighting devices and methods of formingthe reflective layer are provided. The reflective layer may include adielectric layer including one or more insulating materials. Anintermediate layer with robust adhesive properties to the dielectriclayer and a subsequent metal layer may be formed on the dielectriclayer. The intermediate layer may include one or more materials having ahigher enthalpy of reaction than the one or more insulating materials.Because of the higher enthalpy of reaction, atoms of the one or morematerials in the intermediate layer may form bonds with atoms of the oneor more insulating materials. A metal layer may be formed on theintermediate layer to reflect light emitted from an active region of alight emitting diode (LED).

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1 is a cross-section view illustrating an example III-nitride lightemitting diode (LED) device;

FIG. 2 is a cross-section view illustrating forming a dielectric layeron an emission layer;

FIG. 3 is a cross section view illustrating forming an intermediatelayer on the dielectric layer;

FIG. 4 is a cross section view illustrating forming a metal layer on theintermediate layer to form a reflective layer;

FIGS. 5A-5B are transmission electron microscope (TEM) micrographsillustrating a cross section of an exemplary reflective layer;

FIG. 6 is a flow chart illustrating a method of forming the reflectivelayer;

FIG. 7 is a flow chart illustrating another method of forming thereflective layer;

FIG. 8 is a flow chart illustrating another method of forming thereflective layer; and

FIG. 9 is a flow chart illustrating another method of forming thereflective layer.

DETAILED DESCRIPTION

Examples of different light emitting diode (“LED”) implementations willbe described more fully hereinafter with reference to the accompanyingdrawings. These examples are not mutually exclusive, and features foundin one example can be combined with features found in one or more otherexamples to achieve additional implementations. Accordingly, it will beunderstood that the examples shown in the accompanying drawings areprovided for illustrative purposes only and they are not intended tolimit the disclosure in any way. Like numbers refer to like elementsthroughout.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present invention. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

It will be understood that when an element such as a layer, region orsubstrate is referred to as being “on” or extending “onto” anotherelement, it can be directly on or extend directly onto the other elementor intervening elements may also be present. In contrast, when anelement is referred to as being “directly on” or extending “directlyonto” another element, there are no intervening elements present. Itwill also be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present. It will be understood that these terms areintended to encompass different orientations of the element in additionto any orientation depicted in the figures.

Relative terms such as “below” or “above” or “upper” or “lower” or“horizontal” or “vertical” may be used herein to describe a relationshipof one element, layer or region to another element, layer or region asillustrated in the figures. It will be understood that these terms areintended to encompass different orientations of the device in additionto the orientation depicted in the figures.

Semiconductor light-emitting diodes (LEDs) are among the most efficientlight sources currently available. Materials used in the manufacture ofLEDs capable of operation across the visible spectrum include GroupIII-V semiconductors, particularly binary, ternary, and quaternaryalloys of gallium, aluminum, indium, and nitrogen, which may be referredto as III-nitride materials. Typically, III-nitride devices areepitaxially grown on sapphire, silicon carbide, or III-nitridesubstrates by metal-organic chemical vapor deposition (MOCVD), molecularbeam epitaxy (MBE), or other epitaxial techniques. Some of thesesubstrates are insulating or poorly conducting. Devices fabricated fromsemiconductor crystals grown on such substrates may have both thepositive and the negative polarity electrical contacts to theepitaxially-grown semiconductor on the same side of the device. Incontrast, semiconductor devices grown on conducting substrates may befabricated such that one electrical contact is formed on the epitaxiallygrown material and the other electrical contact is formed on thesubstrate. However, devices fabricated on conducting substrates may alsobe designed to have both contacts on the same side of the device onwhich the epitaxial material is grown in a flip-chip geometry so as toimprove light extraction from LED chip, to improve the current-carryingcapacity of the chip, or to improve the heat-sinking of the LED die. Inorder to fabricate efficient LED devices, the contacts may beelectrically isolated from each other such that electrical carriers ofthe appropriate polarity are injected into the p-type and n-type sidesof the semiconductor junction, where they recombine to produce light.

Referring now to FIG. 1, a cross-section view illustrating an exampleIII-nitride LED device 100 is shown. One or more semiconductor layers,including, for example, an n-layer 102, an active region 104, and ap-layer 106 may be epitaxially grown on a substrate 108. A p-contact 110and an n-contact 112 may be formed on the same side of the device asdescribed above. Electrical isolation between the p-contact 110 and then-contact 112 may be achieved by etching a mesa structure 114 into thedevice extending from the topmost layer down into the underlying n-layer102 and forming a separate defined p-contact 110 and n-contact 112. TheLED may be mounted to a submount assembly 116, which may include asubmount on which the LED is mounted with solder bumps. The solder bumpsmay create a gap between the submount and the LED. The connected LED andsubmount assembly may then be encapsulated in a high index of refractiongel or epoxy.

The high index gel or epoxy may be selected to match an index ofrefraction of the substrate 108 as closely as possible, since the lightproduced in the device may be extracted through the substrate 108. Whenlight is incident on an interface between two materials, the differencein index of refraction determines how much light is reflected at thatinterface, and how much light is transmitted through it. The larger thedifference in index of refraction, the more light is reflected. Thus,the small difference between the index of refraction of the sapphiresubstrate and the high index gel or epoxy encapsulating the device mayensure that most of the light generated in the device that reaches theemitting surfaces of the substrate 108 is extracted from the device.

Photons may be generated within the active region 104. Extracting thephotons from the semiconductor active region 104 into the LED packageand outside may difficult due, in part, to the high indices ofrefraction of the semiconductor layers. Photons generated within theepitaxial semiconductor layer may be incident upon either the interfacebetween the semiconductor layers and the substrate 108, the interface ofa wall 122 of the mesa 114 and the high index gel or epoxy in thesubmount assembly 116, or the interface between the semiconductor layersand the metal contacts. Photons incident on any of the three interfacesface a step in material refractive index. Such a step in refractiveindex may cause a ray 118 incident on such an interface to be split intoa transmitted portion 118 a and a reflected portion 118 b. Lighttransmitted out from the wall 122 of the mesa 114 (i.e. portion 118 a)may not be directed out of the device in a useful direction. Thus, lightlost through transmission at the wall 122 of the mesa 114 may contributeto a low light extraction efficiency of the III-nitride LED device 100.

The high index gel or epoxy encapsulating the device may result in asmall difference in refractive index at the interface at the wall 122 ofthe mesa 114 between the semiconductor layers between the contacts andthe submount assembly 116. As a result, much of the light incident onthis area may be transmitted in the direction of the submount assembly,which may cause significant optical loss. As described above, lightextracted in the area towards the submount assembly 116 may not beusefully extracted from the III-nitride LED device 100.

As light propagates through the device, it may be subject toattenuation. Attenuation can occur at all places within thesemiconductor, but is likely to be largest at the interfaces, forexample between the n-layer 102 and the substrate 108; between thesemiconductor layers and the contacts; in the active region 104; and inany nucleation layer present between the n-layer 102 and the substrate108. The further light propagates, the more it is attenuated. Light raystravelling through the semiconductor layer with a large angle β, theangle of propagation relative to the substrate 108, may require a longerpath length to travel a given distance in the semiconductor resolvedparallel to the substrate 108 compared with light rays with a smallangle β. Each time a ray is reflected, the sign of the angle ofpropagation may be reversed. For example, a ray propagating at angle θmay propagate at an angle −β upon reflection. Large angle θ rays maypass a greater number of times through the active region 104 and may bereflected off the various interfaces a greater number of times. Eachtime the ray is reflected, it becomes more attenuated. Such rays maytherefore be subject to greater attenuation per unit distance ofpropagation in the x-direction than rays travelling at shallower anglesβ. Thus, most of the flux (optical power) incident on the wall 122 ofthe mesa 114 is incident at shallow angles β. For a device with someabsorption in the contacts (e.g., a device with an aluminum p-contact),70% or more of the total flux incident on the wall 122 of the mesa 114may be incident at an angle of in the range of approximately −10degrees<β<30 degrees. For a device with a highly reflective p-contact110 such as a pure silver p-contact 110, the proportion of flux incidenton the wall 122 of the mesa 114 within this same angular range may fallto about 60%.

A reflective layer 120 may be used to reflect light emitted from theactive region 104. The reflective layer 120 may compose one or more ofdielectric layers, metal stacks, composite mirrors, or distributed Braggreflectors (DBR). The reflective layer 120 may be formed on the wall 122of the mesa 114 to maximize the reflection of light incident on the wall122 of the mesa 114. The reflective layer 120 may include a transparentconducting layer, a dielectric layer, and a metal mirror. A compositemirror may require the metal mirror to be formed directly on thedielectric layer. The metal mirror may compose a noble metal, such as,for example silver (Ag) or gold (Au). The dielectric layer may composeany insulating material, such as, for example, an oxide or nitride ofsilicon or magnesium fluoride.

It is known in the art that a noble metal, such as Ag, does not adherewell to a dielectric material, such as silicon oxide. The poor adhesionmay introduce problems during fabrication processes and may reduce thereflectivity of the reflective layers. An upper surface of thedielectric layer may be roughened prior to deposition of the metalmirror to increase adhesion. The development of surface features andincreased surface area of the roughened surface may promote adhesionbetween the noble metal and dielectric material, However, this may notbe enough to ensure proper and/or sufficient adhesion. An adhesion layermay be introduced between the dielectric layer and the metal mirror toincrease the adhesion between the two. However, most adhesives layersare optically absorptive and may negatively affect the reflectivity ofthe reflective layer. Accordingly, it may be desirable to improve thestrength of adhesion between the metal mirror and the dielectric layerwhile minimizing the optical impact on total reflectance of thereflective layer 120.

Referring now to FIG. 2, a cross-section view illustrating forming adielectric layer 204 on an emission layer 202 is shown. As describedabove, the emission layer 202 may contain a first semiconductor layer206, an active region 208, and a second semiconductor layer 210. Theemission layer 202 may be formed on a substrate 212. The substrate 212may compose silicon or a crystalline material, such as aluminum oxide,and may be a commercial sapphire wafer.

The first semiconductor layer 206 may compose any Group III-Vsemiconductors, including binary, ternary, and quaternary alloys ofgallium, aluminum, indium, and nitrogen, also referred to as III-nitridematerials. For example, the first semiconductor layer 402 may composeIII-V semiconductors including but not limited to AlP, AlAs, AlSb, GaN,GaP, GaAs, GaSb, InN, InP, InAs, InSb, II-VI semiconductors includingbut not limited to ZnS, ZnSe, CdSe, CdTe, group IV semiconductorsincluding but not limited to Ge, Si, SiC, and mixtures or alloysthereof. These semiconductors may have indices of refraction rangingfrom about 2.4 to about 4.1 at the typical emission wavelengths of LEDsin which they are present. For example, III-nitride semiconductors, suchas GaN, may have refractive indices of about 2.4 at 500 nm, andIII-phosphide semiconductors, such as InGaP, may have refractive indicesof about 3.7 at 600 nm. In an example, the first semiconductor layer 402may compose GaN.

The first semiconductor layer 206 may be formed using conventionaldeposition techniques, such as MOCVD, MBE, or other epitaxialtechniques. The first semiconductor layer 206 may be doped with n-typedopants.

The second semiconductor layer 210 and the active region 208 may composeany Group III-V semiconductors, including binary, ternary, andquaternary alloys of gallium, aluminum, indium, and nitrogen, alsoreferred to as III-nitride materials. For example, the secondsemiconductor layer 210 and the active region 210 may compose III-Vsemiconductors including but not limited to AlN, AlP, AlAs, AlSb, GaN,GaP, GaAs, GaSb, InN, InP, InAs, InSb, II-VI semiconductors includingbut not limited to ZnS, ZnSe, CdSe, CdTe, group IV semiconductorsincluding but not limited to Ge, Si, SiC, and mixtures or alloysthereof. These semiconductors may have indices of refraction rangingfrom about 2.4 to about 4.1 at the typical emission wavelengths of LEDsin which they are present. For example, III-nitride semiconductors, suchas GaN, may have refractive indices of about 2.4 at 500 nm, andIII-phosphide semiconductors, such as InGaP, may have refractive indicesof about 3.7 at 600 nm. In an example, the second semiconductor layer210 and the active region 208 may compose GaN.

The second semiconductor layer 210 and the active region 208 may beformed using conventional deposition techniques, such as MOCVD, MBE, orother epitaxial techniques. The active region 208 and the secondsemiconductor layer 210 may be formed along with the first semiconductorlayer 206 or may be formed separately. The active region 208 and thesecond semiconductor layer 210 may compose a similar semiconductormaterial as the first semiconductor layer 206 or their composition mayvary.

The second semiconductor layer 210 may be doped with p-type dopants.Accordingly, the active region 208 may be a p-n diode junctionassociated with the interface of the first semiconductor layer 206 andthe second semiconductor layer 210. Alternatively, the active region 208may include one or more semiconductor layers that are doped n-type,doped p-type, or are undoped. The active region 208 may emit light uponapplication of a suitable voltage through the first semiconductor layer206 and the second semiconductor layer 210. In alternativeimplementations, the conductivity types of the first semiconductor layer206 and the second semiconductor layer 210 may be reversed. That is, thefirst semiconductor layer 206 may be a p-type layer and the secondsemiconductor layer 210 may be an n-type layer.

It should be noted that the emission layer 202 may take any shape. Forexample, the emission layer 202 may be shaped like a mesa as describedabove with reference to FIG. 1. In another example, the emission layer202 may be segmented from other semiconductor layers and may beseparated from another emission layer by a trench or an isolationregion.

The dielectric layer 204 may be formed on an upper surface 214 of theemission layer 202. The dielectric layer 204 may compose one or moredielectric materials, such as, an oxide, a nitride, or an oxynitride. Inan example, the dielectric layer 204 may compose silicon oxide. Inanother example, the dielectric layer 204 may compose a metal fluoridesuch as magnesium fluoride. The dielectric layer 204 may be formed usinga conventional deposition technique, such as, for example, CVD, plasmaenhanced chemical vapor deposition (PECVD), MOCVD, atomic layerdeposition (ALD), evaporation, reactive sputtering, chemical solutiondeposition, spin-on deposition, or other like processes. The dielectriclayer 204 may have a thickness T₂₀₄ ranging from approximately 100 nm toapproximately 1000 nm. The dielectric layer 204 may be patterned andetched using conventional techniques.

It should be noted that the dielectric layer 204 may be formed on anysurface depending on the configuration of the emission layer 202. Forexample, the dielectric layer 204 may be in contact with the firstsemiconductor layer 206, the active region 208, and the secondsemiconductor layer 210 as seen above with reference to FIG. 1. Inanother example, the dielectric layer 204 may be formed on a lowersurface 216 of the substrate 212. In another example, the dielectriclayer 204 may be formed on a phosphor region (not shown) formed on theemission layer 202 to wavelength convert emitted light.

Referring now to FIG. 3, a cross section view illustrating forming anintermediate layer 302 on the dielectric layer 204 is shown. Theintermediate layer 302 may compose a material with a higher enthalpy ofreaction than the material of the dielectric layer 204. For example, ifthe dielectric layer 204 includes one or more oxides, the intermediatelayer 302 may compose one or more materials having a higher enthalpy ofoxidation than the material of the dielectric layer 204. In anotherexample, if the dielectric layer 204 includes fluoride, the intermediatelayer 302 may compose one or more materials having a higher enthalpy offluoridation than the material of the dielectric layer 204.

The intermediate layer 302 may compose atoms of one or more metallicmaterials, such as for example, Mg, Al, Ge, Ti, Si, Ta, Mn, W, Co, Ni,Cu, Ru, Pd, Pt, and Ag. In an example, the intermediate layer maycompose Al, which may have a negative heat of oxide formation ofapproximately 550 kJ/mol per bond formed to approximately 600 kJ/mol perbond formed. This may be greater than the negative heat of oxideformation of silicon dioxide, which may be approximately 400 kJ/mol perbond formed to approximately 500 kJ/mol per bond formed. Theintermediate layer 302 may adhere well to the dielectric layer 204.

The intermediate layer 302 may be formed using a conventional depositiontechnique, such as, for example, CVD, PECVD, MOCVD, ALD, evaporation,reactive sputtering, chemical solution deposition, plating, spin-ondeposition, or other like processes. The intermediate layer 302 may havea thickness T₃₀₂ ranging from approximately 1 angstrom to approximately50 angstroms. In an example, the intermediate layer 302 may have athickness T₃₀₂ ranging from approximately 5 angstroms to approximately20 angstroms.

Referring now to FIG. 4, a cross section view illustrating forming ametal layer 402 on the intermediate layer 302 to form a reflective layer404 is shown. The metal layer 402 may compose one or more metallicmaterials that reflect light. For example, the metal layer 402 maycompose a noble metal, such as Ru, Rh, Pd, Ag, Os, Ir, Pd, and Au. Themetal layer 402 may compose stacks of one or more of the metalsdescribed above.

The metal layer 402 may be formed using a conventional depositiontechnique, such as, for example, CVD, PECVD, MOCVD, ALD, evaporation,reactive sputtering, chemical solution deposition, plating, spin-ondeposition, or other like processes. The metal layer 402 may have athickness T₄₀₂ ranging from approximately 50 nm to approximately 1000nm. The intermediate layer 302 may adhere well to the metal layer 402.

Upon deposition, and/or in subsequent annealing steps, atoms in theintermediate layer 302 may partially react with atoms from theunderlying dielectric layer 204 and the intermediate layer 302 maybecome optically transparent. Because the intermediate layer 302 mayhave a higher enthalpy of reaction than the underlying dielectric layer204, the atoms that form the adhesive layer may break bonds between oneanother and form bonds with atoms in the dielectric layer 204 Forexample, if Al is used to form the intermediate layer 302 and siliconoxide is used to form the dielectric layer 204, the Al atoms may breakthe existing Si—O bond in the dielectric layer 204 and form a singleAl—O bond. Where the dielectric layer 204 may have had Si—O—Si bonds, itmay now contain Si—O—Al bonds with a dangling bond on the Si that mayterminate with an Al atom.

The enthalpy of reaction serves as a guide to predict which bondsbetween the intermediate layer 302 and the dielectric layer 204. In theabove example, breaking a Si—O bond and forming an Al—O bond isenergetically favorable due to the intermediate layer 302 having ahigher enthalpy of oxidation, thereby enabling the adhesion. Thethickness T₃₀₂ of the intermediate layer 302 may be sufficient toimprove the adhesive force between the dielectric layer 204 and themetal layer 402, but not too thick such that most of the material in theintermediate layer 302 does not react with the underlying dielectriclayer 204. As the atoms on the intermediate layer 302 oxidize and reactwith atoms in the dielectric layer 204, the resulting bonds may produceoxides with a large band gap. This may allow protons emitted from theactive region 208 to pass through the dielectric layer 204 and theintermediate layer 302 with little to no resistance and reflect off ofthe metal layer 402. In other words, because of the large band gap, thedielectric layer 204 and the intermediate layer 302 may be substantiallytransparent to light emitted from the active region 208.

Referring now to FIGS. 5A-5B, transmission electron microscope (TEM)micrographs illustrating a cross section of an exemplary reflectivelayer 404 is shown. FIG. 5A shows the emission layer 202, the dielectriclayer 204, the intermediate layer 302, and the metal layer 402. FIG. 5Bis a magnification of the reflective layer 404 showing the dielectriclayer 204, the intermediate layer 302, and the metal layer 402. As canbe seen in FIG. 5B, atoms of the intermediate layer 302 may have reactedwith atoms of the dielectric layer 204 to form an adhesive bond.

It should be noted that the FIGS. 1-5B show the reflective layer 404formed on epitaxially grown GaN, the reflective layer 404 may be used inall optically sensitive interfaces that require good adhesion between adielectric layer and noble metal. For example, the reflective layer 404may be formed on any surface of a substrate on which one or moresemiconductor layers are formed. In another example, the reflectivelayer 404 may be formed on a phosphor region used to wavelength convertlight emitted from an active region.

Referring now to FIG. 6, a flow chart illustrating a method of formingthe reflective layer 404 is shown. In step 602, a vacuum may be formed.In step 604, the dielectric layer 204 may be formed using one or more ofthe methods described above without breaking the vacuum. In step 606,the intermediate layer 302 may be formed using one or more methodsdescribed above without breaking the vacuum. In step 608, the metallayer 402 may be formed using one or more of the methods described abovewithout breaking the vacuum. In step 610, the vacuum may be broken.

Referring now to FIG. 7, a flow chart illustrating another method offorming the reflective layer 404 is shown. In step 702, a vacuum may beformed. In step 704, the dielectric layer 204 may be formed using one ormore of the methods described above without breaking the vacuum. In step706, the intermediate layer 302 may be formed using one or more methodsdescribed above without breaking the vacuum. In step 708, the vacuum maybe broken. In step 710, the metal layer 402 may be formed using one ormore of the methods described above. In an alternative example, a secondvacuum may be formed prior to performing step 710.

Referring now to FIG. 8, a flow chart illustrating another method offorming the reflective layer 404 is shown. In step 802, a vacuum may beformed. In step 804, the dielectric layer 204 may be formed using one ormore of the methods described above without breaking the vacuum. In step806, the vacuum may be broken. In step 808, the intermediate layer 302may be formed using one or more methods described above. In step 810,the metal layer 402 may be formed using one or more of the methodsdescribed above. In an alternative example, a second vacuum may beformed prior to performing step 808 or step 810.

Referring now to FIG. 9, a flow chart illustrating another method offorming the reflective layer 404 is shown. In step 902, a vacuum may beformed. In step 904, the dielectric layer 204 may be formed using one ormore of the methods described above without breaking the vacuum. In step906, the intermediate layer 302 may be formed using one or more methodsdescribed above without breaking the vacuum. In step 908, the vacuum maybe broken.

Once the vacuum is broken, a native oxide may form on an upper surfaceof the intermediate layer 302. The native oxide may interfere withadhesion between the intermediate layer 302 and the dielectric layer 204and/or the metal layer 402. In step 910, the upper surface of theintermediate layer 302 may be cleaned and prepared to remove the layerof the native oxide. The cleaning and preparation may include anyconventional washing, etching, or planarization process.

In step 912, the metal layer 402 may be formed after the native oxide isremoved using one or more of the methods described above. In analternative example, a second vacuum may be formed prior to performingstep 910 or step 912.

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element can be used alone or in any combination with theother features and elements. In addition, the methods described hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable medium for execution by a computeror processor. Examples of computer-readable media include electronicsignals (transmitted over wired or wireless connections) andcomputer-readable storage media. Examples of computer-readable storagemedia include, but are not limited to, a read only memory (ROM), arandom access memory (RAM), a register, cache memory, semiconductormemory devices, magnetic media such as internal hard disks and removabledisks, magneto-optical media, and optical media such as CD-ROM disks,and digital versatile disks (DVDs).

1. A conductive reflective layer comprising: a dielectric layer on anunderlying layer, a dielectric layer having a first enthalpy ofreaction; an intermediate layer on the dielectric layer; and a metallayer on the intermediate layer, the metal layer and the intermediatelayer electrically coupled to the underlying layer.
 2. The conductivereflective layer of claim 1, wherein the underlying layer iselectrically conductive.
 3. The conductive reflective layer of claim 1,wherein the dielectric layer comprises silicon oxide.
 4. The reflectivelayer of claim 1, wherein the dielectric layer has a thickness rangingfrom 5 angstroms to 50 angstroms.
 5. The conductive reflective layer ofclaim 1, wherein the intermediate layer comprises aluminum.
 6. Theconductive reflective layer of claim 1, wherein a majority of atoms ofthe intermediate layer form bonds with atoms of the dielectric layer. 7.The conductive reflective layer of claim 1, wherein the metal layercomprises a noble metal.
 8. (canceled)
 9. (canceled)
 10. The conductivelayer of claim 1, wherein the metal layer has a thickness ranging from50 nm to 1000 nm.
 11. A method of forming a reflective layer on a lightemitting diode (LED) device, the method comprising: forming a dielectriclayer under a vacuum, the dielectric layer comprising one or moreinsulating materials; forming an intermediate layer on the dielectriclayer under the vacuum, the intermediate layer comprising one or morematerials having a higher enthalpy of reaction than the one or moreinsulating materials, such that atoms of the one or more materials formbonds with atoms of the one or more insulating materials; and forming ametal layer under the vacuum on the intermediate layer.
 12. The methodof claim 11, wherein the dielectric layer is formed on an emission layerof an LED device.
 13. The method of claim 11, wherein the dielectriclayer comprises silicon oxide.
 14. The method of claim 11, wherein theintermediate layer comprises one or more metallic materials.
 15. Themethod of claim 11, wherein the intermediate layer comprises Al.
 16. Themethod of claim 11, wherein the bonds formed comprise O—Al bonds. 17.The method of claim 11, wherein the metal layer comprises Ag.
 18. Themethod of claim 11, wherein the dielectric layer and the intermediatelayer are substantially transparent to light emitted from an activeregion of the LED device.
 19. The method of claim 11, wherein theintermediate layer has a thickness such that a majority of atoms of theone or more materials form bonds with atoms of the one or moreinsulating materials.
 20. The method of claim 11, wherein theintermediate layer has a thickness ranging from approximately 5angstroms to approximately 20 angstroms.
 21. The conductive reflectivelayer of claim 1, wherein the intermediate layer has a second enthalpyof reaction that is greater than the first enthalpy of reaction.
 22. Theconductive reflective layer of claim 1, wherein the dielectric layer ison an emission layer.
 23. A light emitting diode (LED) devicecomprising: a light emitting layer; and a conductive reflective layercomprising: a dielectric layer on an underlying layer, the dielectriclayer having a first enthalpy of reaction; an intermediate layer on thedielectric layer; and a metal layer on the intermediate layer, the metallayer and the intermediate layer electrically coupled to the underlyinglayer.